Significance The goal of this project is to document the co-variation that exists in behavioral, neuroendocrine, and immunological responsiveness to demanding circumstances. We expect to identify constellations of characteristics that reflect individual differences in personality and temperament, and propose that, as in humans, such differences may have health consequences. Objectives In the past budget year, our objectives have been to determine the stability of personality assessments made on our 18 subject animals (adult male rhesus monkeys) in 1993. Animals were observed while 1) watching standardized videotaped displays of behavior performed by unfamiliar animals, and 2) interacting with each other in stable social dyads. Results Our principal focus in these studies has been on the personality dimension [unreadable]sociability[unreadable]. While viewing the videotapes displaying aggressive or affiliative behavior, animals low in Sociability spent more time in the front of the cage, and spent more time staring at the display, compared to animals high in Sociability. To the extent that proximity and greater direct eye contact may be regarded as threatening, this result suggests that low-sociable animals may respond to social initiations with behavior that is more likely to result in conflict, compared to high-sociable animals. In the dyad study, low-sociable animals spent more time in nonsocial activity, and tended to receive fewer social solicitations, compared to high-sociable animals, suggesting that low-sociable animals are perceived as less attractive partners. Future directions These data are the first to suggest that personality characteristics in nonhuman primates assessed originally under very different circumstances, are consistent predictors of social behavior years later. Subsequent research aims to explore the role that personality factors play in physiological arousal (through assessment of plasma catecholamine and cortisol concentrations) during social interaction, and whether such factors might interact with social conditions to influence SIV-disease progression. KEYWORDS personality, temperament, simian immunodeficiency virus, social behavior